The present invention relates to a magnetic disk apparatus having a read/write control circuit for reading and writing data from and to only valid data areas of a selected target data track by skipping void data areas, such as embedded servo areas and magnetically defective areas.
A magnetic disk apparatus is connected to an apparatus, such as a computer, via an interface control circuit. The magnetic disk apparatus includes a read/write control circuit having timing clock generating means to produce a read/write synchronization signal which is supplied to the interface control circuit and used for transmitting read and write data to and from the computer. More specifically, the interface control circuit sends the write data from the computer to the magnetic disk apparatus in synchronization with the read/write synchronization signal in a write mode. Further, the interface control circuit sends the read data from the magnetic disk apparatus to the computer in synchronization with the read/write synchronization signal in a read mode.
The magnetic disk apparatus has one or more magnetic disks. If the magnetic apparatus has a servo surface assigned on one surface of a plurality of magnetic disk surfaces, servo information read from the servo surface is used for generating the read/write synchronization signal. The other surfaces of the magnetic disks are data surfaces having a plurality of concentric data tracks divided into a plurality of sectors.
The data surfaces of the magnetic disks often have one or more magnetically defective areas in which data cannot be recorded. Further, if embedded servo areas are provided at leading portions of the sectors on the data surfaces, the embedded servo areas cannot be used to record data, either (the magnetically defective area and the embedded servo area are referred to as a void data area or void area). Therefore, it is necessary to prevent the data from being recorded in the void area, and not to treat the signal read from the void area as the read data.
A conventional read/write control circuit of a conventional magnetic apparatus always supplies the read/write synchronization signal to the interface control circuit even when the read or write operation is carried out to the void area. This means that the conventional magnetic apparatus has no means to discriminate the void area from the normal or valid data area. Therefore, the interface control circuit is required to discriminate the void area.
To this end, a control circuit for detecting faulty sectors including a void area is disclosed in U.S. Pat. No. 4,405,952. The control circuit stores the address of the faulty sectors in order to discriminate the faulty sectors from normal or valid sectors. If the read or write operation is to be carried out to the faulty sectors, i.e., if the address of one of the faulty sectors is designated, the control circuit changes the faulty sector address into an address of a replacement sector so that the data to be written into or read from the faulty sector is written to or read from the replacement sector.
The conventional manner described above has, however, a disadvantage in that an excessive time period is required to position a magnetic head to the replacement sector. Further, the length of a data unit (logical record) transferred between the computer and the disk apparatus is limited by the memory capacity of one sector. That is, the capacity of the logical record cannot be larger than the memory capacity of one sector.